Variable-load brake



March 4 1924. 1 ,485,487

E. H. DEWSON VARIABLE LOAD BRAKE Filed Jan. 26, 1923 INVENTOR EDWARD H DEWSON ATTORN-EY Patented Mar. #3, 1924.

EDWARD H. DEWSON, OF QUINCY, MASSACHUSETTS, ASSIGNOR TO THE WESTINGHOUSE AIR BRAKE COMPANY, OF WILMERDING, PENNSYLVANIA, A CORZPORATION OF PENNSYLVANIA.

VARIABLE-LOAD BRAKE.

Application filed January 26, 1923.

To all whom it may concern:

Be it known that I, EDWARD H. DEWSON, a citizen of the United States, residing at Quincy, in the county of Norfolk and State of Massachusetts, have invented new and useful Improvements fication.

This invention relates to fluid pressure inder pressure limiting valve device having a diaphragm 2 for operating a valve 3 for controlling the operation of a brake cylindersupply valve 4B which controls the supply of fluid pressure to the brake cylinder 5. The diaphragm 2'is subject on oneside to the pressure of an adjustable coil spring 6 and the spring is adjusted by means a plunger 7 having screw-threaded engage-i ment in a sleeve 8, mounted in the casing 1 and also having screw-threaded engagement with a cap nut 9. I

The cap nut 9 engages a plate 10"sec ured to a guide rod 11. A crank arm structure is pivotally mounted on the casing adjacent to the plate 10 and has three crank arms 12, 13, and 14. The crank arm 12 is adapted to engage the lower end of the rod 11 and the crank arm' 13 is pivotally connected to a piston rod 43 secured to a'piston 15. Said piston is contained'in a cylinder casing 16 which is'provided with a push rod 17 A bell crank 18 is pivotally connected to'the rod 17 and is fulcrumedgon a bracket 44 carried by the" car body. The free arm of the bell crank is adapted to engage a kgnife edge-19'which is mounted at a convenient place on the car truck.

The crank arm'14 is connectedthrough a link 20 with a ratchet bar 21fslidably mounted inthe casing 1 and preferably two in Variable-Load Brakes, of which the following is a speci- Serial No. 615,011.

25, the pawls 22 and 23 being so spaced'that when one pawl'engagesa tooth of the ratchet bar. the other pawl'will be at a mid posit10n between successive teeth of the bar.

By this meansonepawl'will' engage a tooth of the ratchet bar when thebar moves one-half the distance between successive teeth of the bar, so that afineradjustment' may be obtained.

Fluid pressure for simultaneously operating both pistons. 24 and 25 is suppliedby the operation of a magnet'valve device comprising a magnet 26 anda double beat valve 27 and fluid pressure-for operating the piston 15"is controlled by a double beat valve 28 adapted to be operated by a magnet 29.

The coils of the magnets 26 and 29 are connected in parallel in a circuit including a sourceof current 30 and including a plura-lity of switches 81, each contfolledbyithe opening and closing of a plurality of: car

doors 32, so that when any one or all of the car doors areropened, the magnet circuit will'be closed andwhen all of the car doors have been closed, the circuit will be open;

In operation, when the car isrunning along the road, with all of 'the'car doors 32 in closed position, 'as-shownin full lines, the magnet circuit will be open and the magnets 26 and 29 will be deenergized. When magnet 26 is deenergized, the double beat valve 27 is adapted to supply fluid from a source of pressure, such asthe main -reservoir-33 to the pawl pistons 24 and'25, so that said pistons operate to shift-the pawls 22 and'23 into engagement with the teeth of the" r'atchetba-r 21. When magnet 29 is' deenergized,the double beat valve 28 is operated to connect piston 15' to the atmosclosed" and the magnets 26'and 29 energized. The energization of magnet 26 will operate the double beat valve 27 so that the pistons 24 and 25 are connected to the at mosphere, permitting the retraction of the pawls 22 and 23. The rack bar 21 is then free to move. The energization of magnet 29 operates the double beat valve 28 so that fluid is supplied to piston 15 and the cylinder 16 is thus moved relatively to the pieton 15 by fluid pressure so that the rocker arm 18 engages the knife edge 19.

If the load on the car is increased by passengers entering the car, the downward movement 01 the car body relatively to the car truck produced by the increased load causes a movement to the left of the piston and cylinder connections between the rocker arm 18 and the crank arm 13, so that the crank arm 13 is rotated to cause an upward movement of. the plate 10 and thereby an inward movement of the plunger 7 so that the com ression of the spring 6 is increased. When t e car doors 32 are all closed, the magnet circuit is opened and the magnets 26 and 29 are deenergized. The double beat valve 27 is then operated to supply fluid t0 the pistons 24: and 25, so that the pawls 22 and 23 are operated to lock the bar 21 and thus the plunger 7 in its adjusted position, while the double beat valve 28 is operated to vent fluid from piston 15, so that the rocker arm 18 is moved out of engagement with the knife edge 19.

When the brakes are applied, fluid under pressure is supplied to the brake cylinder through a pipe which leads to chamber 36. The pressure supplied to chamber 36 acts on an exposed area of the valve piston 4 and lifts same from its seat, so that fluid is supplied to chamber 37 which communicates with the brake cylinder 5. The pressure supplied to the brake cylinder acts on the diaphragm 2, the chamber 37 being connected to the diaphragm through passage 38, and when the pressure in the brake cylinder has been increased to a predetermined degree, corresponding with the adjustment of the spring 6 in accordance with the load on the car, the diaphragm will be moved, permitting the valve 3 to close. The fluid pressure then quickly builds up on the upper side of the valve piston 4-, said pressure being supplied thereto through a restricted passage 39, so that the valve piston 4; is moved to its seat, cutting OK the further supply of fluid to the brake cylinder.

The brakes may be released when the pipe 35 is connected to the atmosphere, fluid being exhausted from the brake cylinder 5 and chamber 37 ast the check valve 40 to chamber 36 an then through the pipe 35.

If the load on the car is decreased by passengers leaving the car, the plate 10 will be moved downwardly by the raising of the car body relatively to the car truck, permitting the downward movement of the plunger 7, so that the compression of the spring 6 is reduced.

A valve piston 41, subject to the pressure of a spring 42 controls a by-pass from chamber 36 to chamber 37, and it for any reason, the limiting valve device should fail to act, as in case of breakage of the spring 6, for example, then when the pressure supplied through pipe 35 to chamber 36 has been increased to a predetermined degree, the valve piston 41 will be moved from its seat, permitting the flow of fluid from chamber 36 to chamber 37 and thence to the brake cylinder 5.

It is well known that movement of the car body relative to the car truck as the load is increased is not proportional to successive increments in the load with certain types of car springs, such as the elliptic spring, since such car springs ofler increasing resistance to compression as the springs are. compressed under load, so that this relative movement for a given increase in the load becomes less and less as the load increases and in order to secure an adjusting movement of the rocker arm 18 which is always proportional to increments in the load, the engagingface 45 of the rocker arm 18 is made cam shaped, the contour being worked out so that every relative movement between the car body and the car truck for a given increment in the load will result in a uniform adjusting movement of the rocker arm 18.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is

1. In a load brake, the combination with an adjustable mechanism for regulating the, braking power, of a member associated with the car truck, a rocker arm mounted on the car body and adapted to engage said member, a piston cylinder operatively connected to said arm, and a piston in said cylinder operatively connected to said mechanism.

2. In a load brake, the combination with an adjustable mechanism for regulating the braking power, of a member associated with the car truck, a rocker arm mounted on the car body and adapted-to engage said member, a piston cylinder operatively connected to said arm, a piston in said cylinder operatively connected to said mechanism, and means for supplying fluid under pressure to said piston to cause said rocker arm to engage said member.

3. In a load brake, the combination with a brake cylinder and an adjustable mechanism for limiting the maximum pressure supplied to the brake cylinder, of a mem ber for adjusting said mechanism, a rocker arm for operating said member, a cylinder, a piston in said cylinder operatively con nected to said rocker arm, and a rocker arm engageable with the cartruck and operatively connected to said cylinder.

4. In a load brake, the combination with a brake cylinder and an adjustable mechanism for limiting the maximum pressure supplied to the brake cylinder, of a member for adjusting said mechanism, a rocker arm for operating said member, a cylinder,

a piston in said cylinder operatively connected to said rocker arm, and a rocker arm having a cam face engageable with a portion of the car truck and operatively connected to said cylinder, the cam face being so contoured that the adjusting movement of the rocker arm will be proportional to the increments in the load.

In testimony whereof I have hereunto set my hand.

EDWARD H. DEWSON. 

